In what context?
Barrel distortion () results from the compromise(s) made in lens design, most typically, I guess, in designing short focal length range zoom lenses - or wide angle prime lenses.
More expensive examples are often better corrected.
Considering a zoom lens, there is usually a focal length in the range which exhibits the phenomenon least. With a prime, of course, you don't have that option.
Typically exhibited at the edges of the frame, cropping can help.
It can also be corrected to a degree in PP.